Antenna array employing an automatic averaging technique for increased resolution



June 4, 1968 J. BLASS ET AL 3,387,301

ANTENNA ARRAY EMPLOYING AN AUTOMATIC AVERAGING TECHNIQUE FOR INCREASEDRESOLUTION Filed March 31, 1966 4 Sheets-Sheet l fldrea; Eye, 6255?,5565 5.91%!

June 4, 1968 J. BLASS ET AL 3,387,301

ANTENNA ARRAY EMPLOYING AN AUTOMATIC AVERAGING TECHNIQUE FOR INCREASEDRESOLUTION l a 2' 4 2 2 m /2 /4/2 2 2222242626 30 fZiMf/Vf A U/WEEB 1% w49;] /g K 3 w JNVENTORS JUDD 15! 45.9 /9 20 BY MA rrflfn W 0227? /4z5 17J. BLASS ET AL 3,387,301 ANTENNA ARRAY EMPLOYING AN AUTOMATIC AVERAGINGTECHNIQUE June 4, 1968 FOR INCREASED RESOLUTION 4 Sheets-Sheet 5 FiledMarch 51, 1966 June 4, 1968 J. BLASS ET AL 3,387,301

ANTENNA ARRAY EMPLOYING AN AUTOMATIC AVERAGING TECHNIQUE FOR INCREASEDRESOLUTION Filed March 31, 1966 4 Sheets-Sheet 4 6 2 0" 2 f I I l 1 67/48) fi/A fifiy p/v/pi/e 0/ W056 /69 JIEzEb- 70 United States Patent3,387,301 ANTENNA ARRAY EMPLOYING AN AUTO- MATHZ AVERA-GING TECHNIQUEFOR IN- CREASED RESOLUTION Judd Blass, Englewood, and Matthew W. Slate,Teaneclr,

NJ., assignors to Blass Antenna Electronics Corporation, Long islandCity, N.Y., a corporation of Delaware Filed Mar. 31, 1966, Ser. No.539,074 13 Claims. (Cl. 343-100) ABSTRACT OF THE DISCLOSURE An antennasystem comprised of a stationary array of radiating elements and a feedmeans for directing electromagnetic rays toward the array, which raysare reflected from the array and directed into space. The array iscaused to develop a scanning beam by providing control means whichselectively controls the phase delay imparted to the electromagneticwaves impinging upon each element of the radiating array therebydeveloping a scanning beam of relatively narrow beam width. Since thechanges in phase delay between adjacent radiating elements is astep-like pattern as opposed to a linear phase taper, the resultant beampointing error and sidelobe variation is minimized through theapplication of a signal simultaneously applied to all elements of thearray which signal varies in magnitude at a rate at least equal to therepetition rate of electromagnetic wave pulses directed toward theradiating array from the feed means.

The instant invention relates to computational methods and apparatus,and more particularly to novel computational methods and apparatusespecially adapted for use in radar systems which act to effectivelyeliminate beam pointing error and unwanted sidelo'bes in transmitledradar signals so as to significantly enhance the quality and value ofreturning radar signals, thereby enhancing overall operation of suchradar systems.

Typical radar systems are conventionally comprised of a signal pulsesource which is arranged to direct the generated electromagnetic wavesto impinge upon a refiecting dish antenna, usually of parabolic surfacecontour, which reflects the electromagnetic waves, directing themoutwardly and away from the parabolic dish, with all of the outgoingwaves being substantially parallel to one another. The signal source andparabolic reflector are typically mounted upon a rotatable platformwhich acts to rotate the antenna assembly at a predetermined number ofrevolutions per minute. Radar antenna assemblies of this type areusually quite large and require very large spherical shaped enclosuresso as to freely permit rotation of the entire antenna assembly. Inaddition thereto, practical limitations of the assembly structureseverely limit the number of sweeps or revolutions per unit time whichthe assembly may perform. All of these practical limitations have beenovercome through use of a novel antenna structure which is completelystationary and has no moving parts.

Antennas of this novel class are described in detail in copendingapplications Ser. No. 244,089, filed Dec. 12, 1962, now Patent No.3,274,601, and Ser. No. 409,905, filed Nov. 12, 1964, Judd Blass et al.,and which have been assigned to the assignee of the instant invention.One category of such antennas are normally comprised of a plurality ofradiating elements arranged in either a linear or a planar array, witheach of the individual radiating elements having first open ends andsecond sealed ends, and a plurality of electronically controlledshort-circuiting devices such as, for example, semiconductor diodesmounted inwardly from the open end of each waveguide 3,387,301 PatentedJune 4, 1968 ice section and being spaced from one another by fractionsof a wavelength A where is equal to the wavelength of the operatingfrequency f of the antenna, which operating frequency f may be typicallygreater than 1 megacycle. Each of the radiating elements are also spacedfrom one another by some fraction of a wavelength.

in planar arrays, the signal source providing the electromagnetic wavesis positioned in front of the planar array, with all of the open ends ofthe waveguide sections confronting the signal source. The emittedelectromagnetic waves move toward the planar array and enter into theopen ends of all of the individual waveguide sections. Theelectromagnetic waves enter into each Waveguide section, are reflectedat the sealed end thereof, and leave each waveguide section to enterinto space and move toward a sector in space.

A phase delay is experienced by each electromagnetic wave, which phasedelay is equal to twice the depth in wavelength of each waveguidesection, since the electromagnetic wave enters each waveguide section,is reflected at the rear end thereof, and leaves each waveguide sectiontravers ng the length of the waveguide section twice. Since thewaveguide sections in the planar array are all positioned at differingdistances from the energy source, additional phase delay will beintroduced to the electromagnetic waves equal to the difference indistances of each of the sections of the array from the energy source.This phase delay may be substantially compensated for by making thosewaveguide sections which are further removed from the wave generatingsource shorter in electrical length so that the sum of the phase delayintroduced by the waveguide section plus the phase delay introduced bythe differing distance from the wave generating source will besubstantially equal for all of the waveguide sections over the entireplanar array. Thus, the electromagnetic wa-ve source and planar arraysimulate conventional radar antenna arrays comprised of a wavegenerating source and a parabolic dish reflector.

In order to simulate the rotational capability of conventional radarantenna assemblies, each of the waveguide sections are provided with aplurality of short-circuiting elements, or semiconductor diodes, as werepre viously mentioned. It is possible through a central electroniccontrol means to selectively energize one of the group ofshort-circuiting elements in each of the waveguide sections in order toalter the phase delay for each waveguide section. By appropriateelectronic control it therefore becomes possible to collimate theradiation produced by each element so that the antenna radiatespredominantly in a particular direction. This control is carried out byx and y input information signals coupled to the radiating elements.

The x input information sets up a cone-shaped radiation pattern havingits apex at the intersection between the x and y axes of the planararray front face and having its longitudinal axis coincident with the x"axis. The taper of the cone is defined by the angle a.

The y input information sets up a second cone-shaped radiation patternhaving its apex at the intersection between the "x and y axes of theplanar array front face and having its longitudinal axis coincident withthe y axis. The taper of the second cone is defined by the angle 5.

The intersection between the surfaces of the first and second conesdetermines the direction of radiation (on and 5) from the planar array.The half of the cone surface of each of the cones which lies behind thefront surface of the planar array may be ignored since radiation occursin only one direction.

If desired, the interior angle of one cone may be kept constant whilethe interior angle of the other is varied, or the interior angles ofboth cones may be changed simultaneously. It should be noted that theinterior angles of both cones must be altered when an azimuthal sweep atone elevational angle is desired.

It is thereby possible, through use of the planar array and anelectronic control circuit described above. to provide either anindependent azimuthal or elevational scan or a combined azimuthal andelevational scan in order to detect fixed or moving objects, and totrack aircraft, ships or other moving objects. In the quiescent state,the planar array antenna continually sweeps the horizontal and/or thevertical directions in search of objects of interest. Once the presenceof an object of interest is detected by the radar system, it is mostimportant to be able to provide the most accurate data possible toidentify location and speed of the singular or plural objects.

Once the azimuthal and elevational position of an object is determinedas a result of the sweep operation. it is possible, through theelectronic control circuitry, to instantaneously depart from thecontinuous scanning state and lock the antenna in upon the observedflying object. The radiation pattern transmitted into space is comprisedof a single or main lobe of relatively small solid angle which is alsoaccompanied by a plurality of side lobes which, though unwanted, dooccur as part of the radiation pattern and act to produce spuriousreflections from objects illuminated by the side lobes, which may beconfused with the signal which returns to the antenna planar array afterreflection from the moving object. Such side lobes are present eventhough antenna optimum design techniques are employed so as to minimizethe strength of the side lobes and hence to minimize their harmfuleffects.

The electronic control of the phase front effectively acts to angularlyorient the main lobe so as to point its longitudinal axis directly atthe detected object. The angular orientation of the main lobe iscontrolled by the equation:

"\ m 1 cos "ijn 2 COS mn n) where a and B represent the angles which themain lobe makes with the horizontal and vertical axes, respectively,

and

The planar array which is comprised of a matrix of ra- W=sphericalcorrection factor diating elements, is preferably arranged in regularmatrix fashion having a in columns and 11 rows, where one row and onecolumn (usually centrally located) may be arbitrarily selected as thereferences from which the numbers i and j are measured.

The scan angle for the antenna assembly measured from the x and y axesare a and B, respectively. The phase taper (uniform increases in phasefrom row to row or column to column) of K cos 0: or K cos p, which arethe signals coupled to the individual radiating elements for selectivelycontrolling the activation of the radiating elements short-circuitingdevices, control the scanning of the beam. Absolute phase has nosignificance and only the phase difference has any effect on thestructure. K, and K are constants which take into account elementspacing and wavelength.

The antenna is electrically collimated to focus radiation at the antennafeed by the spherical correction function W(i, which provides a phaseadvance for each element to compensate for the varying distance from theradiating elements to the antenna feed. The spherical correctionfunction is so selected that the phase delay corresponding to thedistance from each element to the feed. plus the phase delay minusW(i,j) is a constant.

The three signals required for each radiating element at the ith columnand jth row are, therefore, 1K cos at, 1K cos /3 and W(i,j). If thesethree signals are added. the sum iK cos cz+jK cos ,8+W(i,j) is theprecise phase required at the element 1, j to point the beam in thedesired direction. It should be noted that in all arithmetic operationsfactors of Zn are dropped. The above terms l are generated in binaryfashion and, through suitable binary converting means, are interpretedby each radiating element in order to activate the appropriateshortcircuiting element in order to selectively point the antenna.

As a practical matter, the number of binary bits for which a radiatingelement digital (i.e., discrete step) phase shifter can be constructedis limited. Therefore, the output signals from the radar assemblyelectronics, commonly referred to as the beam steering computer, whichgenerates the signals, are truncated (i.e., reduced) to this number. Inother words, the function of truncation consists of dropping the leastsignificant binary bit positions which extend beyond the accuracycapabilities of the'array. Typical large planar arrays normally employno more than two or three binary bits. This truncation produces an errordistribution over the array. The theoretically continuous or constantvariation of phase with displacement in any direction along the array ireplaced by a distribution with step variations, which approximate theideal continuous variation.

The error distribution is not periodic, and, therefore, to a greatextent, cancels out. But the error distribution still causes a beampointing error and side-lobe variation which is a function of nominalbeam positions.

In a typical beam steering computer, the multiplied binary scan signals,z'K cos a and jK cos B are truncated before these terms are summed withW (i,j). If the input signals representing beam angle are multiplied bya continuum, the ideal outputs would vary in linear fashion, and thetruncated outputs would have distributions with step variations similarto that produced on the antenna aperture by aperture quantization. Thefact that the multiplication is by integers only will, for some inputs,obscure this error distribution and for others, a periodic errordistribution occurs before summation can result. Therefore, thequantization which takes place before addition must be substantiallyfiner than the aperture quantization for a tolerable degradation ofantenna performance.

in order to correct for beam fine pointing variations, a signal A isadded to the binary signal for each radiating element. This is definedas Isophase signal because it is constant over the aperture at any time.This signal will have no efiect on nominal beam angles a and ,3 becauseit does not affect the phase tapers. If the signal A is added beforefinal (aperture) quantization (finer than the aperture quantization),variation in this signal will vary the distribution of finalquantization errors. While the Isophase signal A will not vary themagnitude of step variations in phase, it will shift the points on theantenna aperture at which these steps occur. If a large number ofdifferent Isophase signals are applied (meaning that the Isophase signalis introduced at a point much finer than the aperture quantization), andthe resulting radiation patterns are averaged, the beam pointing errorsand peak side-lobes will tend to cancel out. The resulting signals arethen averaged, whereby the resulting average beam error and side-lobelevel will be substantially less than the peak values which occur in theabsence of the Isophase signals. The average values may be furtherimproved by increasing the number of wave pulses transmitted to stillfurther smooth out the average errors.

The instant invention is thereby characterized by providing electroniccontrol means for producing the angular orientation terms K cos 0: and Kcos ,3 in binary form, multiplying those signals of all integerscorresponding to the values of i and j for each of the radiationelements of the array contained in the m columns and n rows, where i isthe number of a particular column and j is the number of a particularrow and where each of these signals are quantized to P bits; generatingIsophase signals A in binary form, quantized to q bits, and generatingthe :ltpherical correction factor W(i,j) in binary form quantized to rbits. The Isophase signals A are added to each of the products iK cos 0cand K cos ,3, where the Isophase signals added to the products iK cos aare constant for all values of i and may or may not be the same as theIsophase signals added to the products jK cos 5, which are identical forall values of j. The summations are truncated to 1' bits, and the threer bit signals corresponding to each element at column i and row j areadded, with the sum being quantized to s bits, where s is equal to orless than 1'.

The quantization of the above terms is performed by any one of aplurality of round-off procedures. For example, let it be assumed thatthe number 0.56938, which contains five digits, is to be quantized so asto have a length of three digits. One round-off rule which may beapplied is if the most significant bit next to the round-off bit isgreater than 5, then the round-off bit is increased by 1. Another rulewhich may be employed is if the most significant bit next to theround-off bit is greater than 4, then 1 is added to the round-off bit.Thus, in the example given using either of these two rules, thequantized result would be 0.569. If the number was to be quantized to 4bits, the result would be 0.5694. In quantization involving binarynumbers, the round-off may be performed by adding 1 to the round-off bitwhen the most significant binary bit being dropped is in binary 1 andkeeping the round-off bit the same when the most significant binary bitbeing dropped is binary 0. The other rule which may be employed is thatof simply making no change whatsoever to the bit being rounded off,regardless of the state of the most significant binary bit beingdropped. By alternating between these two possible selections, this willaffect the finally quantized signal supplied to each radiating element,thereby altering the points on the antenna aperture at which the phasedelay steps will occur. By averaging the returning signals for these twoconditions, it is thereby possible to reduce the resulting average beamerror and side-lobe level, thereby enhancing the significance of thedata returned.

As an alternative embodiment, it should be noted that for any pair ofinput signals K cos 0c and K cos [3, there will be certain Isophasesignals A which will produce minimum error, and that these optimumIsophase signals will vary with variations in K cos a and K cos ,8. Itis possible to compute the relationship between the input signals andthe optimum Isophase signals. If this relationship is a simple one, acomputational device may be provided to generate and apply the optimumIsophase signals dependent upon the values of the input signals K cos aand K cos B. If the relationship becomes more involved, a pre-computedtabulation, which can be stored in the computer for table look-upprocedures may be employed. Thus, as each input signal K cos a and K cos8 is received for providing the antenna beam steering information, thisinput signal data is then examined and the optimum Isophase signal A isthen selected and appropriately summed thereto.

In a preferred embodiment described wherein a plurality of pulsesaretransmitted and the resulting radiation patterns are averaged, in orderto obtain slightly differing beam patterns, all of which havesubstantially the same phase taper, the Isophase signal A is alteredslightly before the generation of each of the pulses thus axiallyshifting the wave front. For example, the Isophase signal generatingmeans which is either manually-or automatically controlled may be adevice which generates digital signals in a pre-prograrnmed or randommanner, or an analog signal generating means such as a random signalgenerator means, a sinusoidal signal generator means, or a linear rampgenerator means generating a constant changing analog Isophase signal,which is then converted into digital forrn by a suitable A to Dconverter means. Since the Isophase signal A varies somewhat for eachtransmitted pulse, its binary representation will vary, causing thebinary information to the radiating elements to be altered slightly forsubsequent pulse. However, due

to the nature of the Isophase signal that is coupled to every radiatingelement within the planar array, the phase taper will remainsubstantially unaltered, but the discrete step variations betweenadjacent radiating elements, while not varying the magnitude of the stepvariations, will shift the points on the aperture at which the stepsoccur. When a number of such pulses are transmitted, each having aslightly differing Isophase signal A are all averaged together, theresulting average beam pointing error and peak side-lobe level will besubstantially diminished so as to yield much more accurate data on theflying object being detected.

It is, therefore, one object of the instant invention to provide a novelradar antenna system having circuitry capable of providing tracking dataof moving objects which is more accurate than that produced byconventional antenna systems.

Another object of the instant invention is to provide a novel radarantenna system capable of scanning moving or fixed objects withoutimparting any physical motion to the antenna structure and furtheremploying an Isophase signal for altering the phase front of the antennato enhance the accuracy of the angle data.

Another object of the instant invention is to provide a novel antennasystem for detecting or tracking objects which is comprised of anantenna assembly which experiences no physical movement throughout theoperation, and which employs electronic control means coupled with anarray of radiating elements and a feed means for simulating themechanical sweep of conventional antenna systems, and being furthercomprised of Isophase signal generating means for further enhancing theaccuracy of the data developed by the system.

These and other objects of the instant invention will become apparentwhen reading the accompanying description and drawings in which:

FIGURE 1 is a perspective view showing in simplified block diagram forman antenna system embodying the concepts of the instant invention.

FIGURE la is a perspective view showing the radiation pattern generatedby a planar array under control of x input signals.

FIGURE 1b is a perspective view showing the radiation pattern generatedby a planar array under control of y input signals.

FIGURE 10 is a perspective view showing the resulting radiation patterngenerated by a planar array under control of both x and y input signals.

FIGURE 2 is a front view of the antenna planar array of FIGURE 1.

FIGURE 3 is a schematic diagram showing the internal structure of two ofthe radiating element sections of the antenna structure of FIGURES 1 and2.

FIGURE 4a is a plot showing the phase changes occurring in an antennaarray of linear aligned elements for two different values of Isophasesignals.

FIGURE 4b is a plot considered in conjunction with FIGURE 4a showing thechanges in phase residues as a result of two different Isophase signalsFIGURE 5 is a block diagram showing the electronic control circuitryemployed for generating the varying phase fronts to produce beamscanning.

FIGURE 5a is a block diagram showing one manner in which the Isophasesignal may be generated.

FIGURES 5b and 5c are waveforms useful in describing the operation ofthe circuit of FIGURE 5a.

FIGURE 6 is a plot showing the phase across an antenna array as aquadratic function of distance from the vertical axis and the phasejumps resulting from an addition of one value of Isophase signal AReferring now to the drawings, FIGURE 1 shows an antenna system 10 whichembodies the principles of the instant invention. The specific antennaarray is described in detail in copending US. applications Ser. No.244,089, entitled, Antenna System, filed Dec. 12, 1962 by J. Blass l andSer. No. 409,905, entitled, Antenna System With Increased BandwidthCapabilities filed Nov. 12, 1964. by I. Blass, both of whichapplications are assigned to the assignee of the instant invention.

For purposes of understanding the instant invention, it is suflicient tounderstand that the antenna assembly is comprised of a feed 11 which isdesigned to direct an electromagnetic wave front 12 toward a planararray 13 comprised of a plurality of individual radiating elements 14which are preferably arranged in a regular matrix fashion comprised ofin columns and 22 rows, as shown in FIGURE 2. The front end 140 of eachradiating element 14 is open, allowing the electromagnetic wavesradiated from feed 11 to enter into the open end and to move in thedirection shown by arrows 15 and 16. as can best be seen in FIGURE 3.The rear end 14b of each radiating element is sealed with the sameconductive material forming the radiating element so as to cause anyelectromagnetic waves reaching the rear end 14b to be reflected so as tomove in the reverse direction, as shown by arrow 17 and leave eachelement. The depth of each radiating element 14 is typically measured inwavelengths or fractions thereof, where is the wavelength for theoperating frequency f of the antenna structure such that f is equal toHA. Thus, the electromagnetic wave in entering each radiating element,being reflected at its rearward end l4b and leaving the radiatingelement, undergoes a phase delay which is equal to twice the depth ofthe radiating element which is measured in wavelengths A. While theantenna system of FIGURE 1 shows a planar array of radiating elements,it should be understood that a linear array, i.e., a single row ofradiating elements. may be employed, if desired, depending only upon theneeds of the user. Such linear arrays may preferably receive radiationat one end of the array and may be staggered in the fashion shown inFIGURE 3 so as to correct the phase delay which the signal undergoes insuch a linear array, which is set forth in detail in above mentionedapplication Ser. No. 244,089.

Each radiating element 14 is further comprised of a plurality ofshort-circuiting elements, conductors l8 through 180 which may, forexample, be semiconductors. each of which are electrically coupledbetween the upper and lower surfaces of the radiating element and arepositioned predetermined distances apart which are usually of the orderof fractions of a wavelength such as, for example, /sx, AA, and soforth. The phase delay which the electromagnetic wave undergoes inentering being reflected and leaving each radiating element may beelectronically modified by selectively energizing i.e., shoitcircuitingone of the short-circuiting elements 18 through 18c. For example, let itbe considered that the electromagnetic wave moves in the direction shownby arrow 15 to enter the upper radiating element 14, shown in FIG- URE3. Let it also be assumed that the short-circuiting elements 18 in theupper element is activated. The entering electromagnetic wave will thenbe confronted with a short-circuited condition at location 18 and willbe reflected, as shown by arrow 19, so as to move out of the radiatingelement and in the direction shown by arrow 17. Thus, it can be seenthat the phase delay imparted to the electromgagnetic wave entering intothe upper radiating element 14 of FIGURE 3 can be substantially reducedby energizing one of the active elements 18 through 180, all of whichare located well in front of the rear surface 14b of the radiatingelements. By energizing the active element 18a in the lower radiatingelement assembly of FIGURE 3, the entering electromagnetic wave movingin the direction of arrows l5 and 16 will be reflected at 18a and movein the direction shown by arrows 19 and 17, respectively, with theactive elements 18 and 18:: being energized in the upper and lowerradiating sections 14, respectively. The points of substantiallyidentical phase will be represented by the phase fronts 20 and 21,thereby establishing a phase taper substantially iii as represented byphantom line 22. It can clearly be seen that the phase fronts changediscretely in step-like fashion and not smoothly, as shown by phantomline 22, but a simulated phase taper will nevertheless be seen to existif adjacent radiating elements to those shown in FIGURE 3 are controlledin a like manner.

The reverse phase taper, as shown by phantom line 23, may be produced byselectively activating the active elements 18a and 18 in the upper andlower radiating elements. respectively, thus developing the phase fronts124 and 25, respectively, substantially resulting in the phase taper 23.

The antenna feed 11 is supported by any suitable structure {not shown),and receives electromagnetic energy from source 26 which generateselectromagnetic waves moving in the direction of the planar array 13.The planar array T3 of radiating elements 14 are electrically coupled tothe output 27a of a beam steering computer 27 which is comprised of theelectronic control circuitry for selectively activating the activeelements (i.e., semiconductors) in each of the radiating elements. Byselective operation of the active elements, the beam direction iscontrolled by planar array 13 in the manner shown in FIGURES in, lb and1c. For example, considering FIGURE 1a, each of the radiating elementsare controlled by x input signals to set up a radiation pattern which isrepresented by the cone-shaped surface 28 which has its longitudinalaxis coincident with the x axis of the planar array and which has itsapex 28a lying at the intersection between the x and 3/ axes of theplanar array. It should be noted that one half of the cone shapedpattern lies behind the front surface of the planar array and thereforehas no effect upon the resultant pattern. Control of the radiatingelements by the x inputs determines the taper or angle x, of the cone.Control of the x inputs permits the taper cf the cone 23 to be narrowedor widened in accordance with the required beam direction.

FIGURE lb shows the radiation pattern which is obtained by control ofthe radiating elements through the inputs. This radiation pattern is acone shaped surface 29 having its apex 29a at the intersection of theplanar array x and y axes. The longitudinal axis of cone 29 iscoincident with the y axis. The taper or angle y; of cone .29 may beincreased or decreased by application of the appropriate y input signalsto the radiating elements.

FIGURE 10 shows the cones 28 and 29 resulting from application of boththe x and y input control. The intersection of the cone surfaces (whichis a straight line) represents the direction of the main lobe of theradiation pattern which is transmitted by the antenna.

For example, if the angles x and y are each then the intersection is astraight line which lies in the surface cf the planar array at a 45angle to the x (or y) axis. This is represented by vector 5:; shown inFIGURE 1.

As the sum of the two angles x and y increases beyond the intersectionbetween the two cones is two straight lines. one directed to the rearand one directed to the front of the planar array. The rearwardlydirected vector may be ignored.

Vector 30 represents a forwardly directed intersection for the casewhere the sum of the angles x and y is greater than 90 (see FIG. 1b).The vector 30 may be represented by three component vectors 30a, 30b and30c. Vector 30a is directed along the y axis. Vector 30b is colinearwith the Z axis (which axis is perpendicular to the xy plane). Vector30c is colinear with the x axis.

The sweep of vector 30 may be controlled in three different ways. Theangle x of the cone 28 may be kept constant while the angle y of thecone 29 may be varied; the angle y of the cone 29 may be kept constantwhile the angle x, of cone 28 is varied; or the angles x and y of cones28 and 29, respectively, may be simultaneously varied. Any one of thethree forms of control may be employed to obtain any desired sweep ofthe main lobe.

The individual radiating elements are selectively operated to controlthe activation of one (or more) of their impressed upon the electroniccontrol means (not shown) of each of the radiating elements. The mannerin which the final binary coded information for each radiating elementis formed is in accordance with the phase equation:

The scan angle from the horizontal and vertical (i.e., x and y axes) areon and ,8, respectively. A phase taper of K cos a or K cos B will causethe beam to be scanned at angles a or ,B, respectively. K and K areconstants involving element spacing and wavelength.

FIGURE 5 shows the beam steering electronics. The scan control 41develops the basic beam steering commands. The horizontal command is aparallel word, typically of eight to ten binary bits. The mostsignificant bit is the coeificient of 1r in the binary expression of thephase taper required along the horizontal axis. The numerical value ofthis word is the phase required in terms of the wavelength A, and isequal to 2a/7\ cos X (2), where a is the distance between adjacentradiating elements (see FIGURE 2). Similarly, the vertical command is abinary parallel word of approximately equal length. The most significantbit is the coefficient of 71' in the binary expression of the phasetaper required along the vertical mis. The numerical value of thismulti-bit word is the phase required in terms of A and is equal to 217/A cos B (3) where b is the distance between adjacent radiating elements(see FIGURE 2).

The antenna is electrically collimated to focus radiation at the feed bythe spherical correction function W(i, j) which is a phase advance foreach element to compensate for the varying distance from the radiatingelements 14 to the feed 11. This function is so calculated that thephase delay corresponding to the distance from each element to the feed,plus the phase delay W(i, j) is a constant.

In order to clearly define the signals which each radiating element 14is to receive, the elements of the planar array (when a planar array isemployed) are numbered in accordance with reference axes. One row andone column are arbitrarily chosen as the reference axes from which thenumbers 2' and j are measured, where z and j are integers. For example,considering FIGURE 2, the reference axis may be considered to be themiddle column m and the middle row n. Values to the right and left ofcolumn m are positive (+1) and negative (i), respectively, while valuesabove and below row n are positive (+1) and negative (j), respectively.

Three signals are required for each element with the radiating elementin column i and row 1' receiving the signals iK cos 0:, 1X cos B andW(i, j). These three signals are added to yield the sum This sum is theprecise phase required in element i, to point the antenna in thedirections a and ,8. It should be noted that in all arithmeticaloperations, factors of 2 may be dropped.

In practice, the number of binary bits for which a digital (discretesteps) phase shifter can be built is limited. Therefore, the outputsignals from the beam steering computer are finally truncated to thislimited member of binary bits. Typical large planar arrays use from twoto three binary bits, but it should be understood that more or less thanthis number can be employed. The use of a two to three binary bit outputsignal produces an error distribution over the planar array. Thetheoretically continuous variation of phase with displacement in anydirection along the array is replaced by a distribution with stepvariations, which distribution approximates the ideal continuousvariation.

The phase of a given element in an optically fed array can be expressedas a function of four variables as given in the following equation:

Phase of element (m,

ricos-ln cos B+W(m, n)

W(m, n) is the quadratic phase correction for the finite focal distance.It has been shown by us, that use of coarse phase control e.g. degreephase increments is possible without pattern deterioration because ofthe quasi-randomizing of the phase residues by the integration of thisquadratic phase term into the beam Steering computer arithmetic.

The terms in the above equation which contain m and n separately are thephase variables required to steer the beam at the angles correspondingto the direction cosines cos a and cos B. The phase reference at thecenter of the antenna is A and in the case of analog drive systems hasnever been considered a variable in the phase control of the antenna.The special purpose beam steering computer performs the arithmeticfunction of adding these four phase terms, discarding multiples of 2,and rounding off the resultant to the nearest integral multiple of thesmallest phase increment. It can be seen that if the quantization is notinfinitesimal, i.e. analog, the value of the constant phase term A willaffect the rounding off resultant.

The results of both a mathematical analysis and an experimentalinvestigation has shown that it is possible to scan the perturbing sidelobes due to the phase quantization residues without scanning the mainbeam itself and thus eliminate the beam pointing errors due to thesephase residues. This is accomplished by varying A in steps equal to afraction of the smallest phase quantization.

For example, the calculated rms beam pointing error of a 25 milliradianbeamwidth antenna test Was approximately 0.35 milliradians with peakerrors as great as 1.2 milliradians. The average error at any beampointing direction could be reduced to nil by cycling A between zerodegrees and 45 degrees in this case by one phase increment. Thesidelobes could be varied from l5 db to -24 db even though thetheoretical sidelobes in the absence of any phase error was -22 db.

The quantitative explanation for this phenomenon can be sen from thediagram shown in FIG. 4a. This shows a graph of the phase distributionacross a linear aperture for two values of A and a single scandirection. It is seen that the adjacent phasors will jump to the nextphase increment at different points along the array for the cases shown.The phase residues which are the difference between the ideal phasecurve and the step phase function is plotted on the base line of thisdiagram and is designated as FIG. 4a. If this phase residue isconsidered to be a periodic wave, its phase is a function of A which canbe made to vary from 0 degrees to 360 degrees by varying A from 0degrees to 45 degrees. Since the phase of the radiation due to thisresidue, with respect to the phase of main beam, can be varied, theinterference of the phase residue on the beam pointing and on the nearsidelobes can also be made to cycle.

For example, if the normal close-in sidelobe of the antenna is 25 db,and the value of a perturbing sidelobe is 31 db, the peak value of theinterference between the two sidelobes may go to 21.5 db, but the rmsinterference would only go to 24 db. In a search mode in which severalhits are placed on a target, with Isophase variation between hits, itwould be possible to keep the sidelobe level to 24 db for the aboveexample; whereas in the absence of Isophase Control a 21.5 db sidelobewould occur for some angles of scan under the same conditions ofinterference.

The additions to the beam steering computer equipment which can provideIsophase Control as herein indicated can also be made to vary the cyclephase through receiver noise.

The additional by-product of this lsophase Control is to cycle eachphasor even though the main antenna beam is not moving. This equalizesthe energy impinging on a phasor in all phase states. Another by-productwhich may be conjectured at this time is the effect of additionalcycling on surface currents which are normally generated in a phasedarray. The use of an optical source feed and quadratic phase correctioneliminates the surface waves that are excited if the phase distributionwere completely uniform. The addition of the Isophase Control, however,

can also smooth out the residual surface currents which do exist andminimize the normal hot spot derating caused by these currents.

In a typical beam steering computer, the scan signal terms K cos a and Kcos ,8 are multiplied by the appropriate column and row numbers i and j,respectively, and the resulting terms iK cos 0: and iKg cos ,6 aretruncated before being added together. For example, the terms iK cos ozand jK cos ,8 may each be ten binary bits in length. Before the additionstep, they are reduced in length to sixbinary bits, for example. If theinput signals K cos cc and K cos B were multiplied by a continuum, theideal outputs would vary in linear fashion and the truncated outputswould have a distribution with step variations similar to that producedon the aperture by aperture quantization. The fact is that themultiplication by integers (i and j) only will, for some outputs,obscure this error distribution, but for others a periodic errordistribution can result. Therefore, the quantization before additionmust be substantially finer than the aperture quantization for atolerable degradation of the performance.

FIGURE 5 is a schematic diagram showing the electronics employed forcontrolling beam position. The circuitry 40 is comprised of a scancontrol 41 which develops the basic beam steering commands which are theterms 2a/ cos 0: and 2b/ cos ,9, which have been previously described.The scan control circuit 41 is comprised of two 8-bit shaft encoders 42and 43 generating a gray code output. The outputs of these shaftencoders are coupled to gray-to-binary decoders 44 and 45, respectively,to deliver two independent scan signals at the operators control. Thebeam can be manually slewed in one or both coordinates by this means.The scan generator 46 is comprised of a clock-pulse generator 47 whichtriggers an 8-bit binary divider 48 which, in turn, develops an 8- bitbinary word at its output terminals to provide a digital bit-by-bit scanof the entire 140 sector covered by the antenna along either principalaxis. Switch means (not shown) electrically connected to the dividercircuit 48 may be provided for the purpose of permitting coarse scansteps with as many as desired of the 8 bits being fixed. If it isdesired to scan one output and slew the other output, the switch means49 may be employed so as to couple the X scan control output to thegray-to-binary encoder 44 and the Y scan output to the binary dividercircuit 48. By operating switch means 49 in the reverse direction fromthat shown, the X output is coupled to the binary divider 48 and the Youtput is coupled to the gray-to-binary encoder 45. This arrangementthereby permits a scan along one principal axis with the position alongthe other being set. If desired, both outputs X and Y may be taken inparallel from the binary divider. This could be done simply bymaintaining lower iWllCl'l arm 4% in the position shown in FIGURE 5 andcoupling upper switch arm 49a to the output of divider 48 and decouplingit from the output of gray-to-binary encoder 44.

The sweep may be maintained indefinitely with the binary divider circuitautomatically resetting itself after reaching its maximum capacity. Theshaft encoders 42 and 83 may be set either manually or automatically. Inorder to provide the capability of instantaneously tertninatingcontinuous sweeping for the purpose of obtaining a fix on a particularobject which has been detected, the binary state of divider circuit 48is ascertained, and the shaft angle encoders 42 and 43 are automaticallyset to provide the proper X and Y output signals to as to fix theantenna system to point toward the desired sector in space. Thiscircuitry has not been described in detail herein, as the capabilityafforded by such circuitry lends no novelty to the device of the instantinvention. For a description of this circuit, see application Ser. No.230,358, filed Oct. 15, 1962.

The output signals representative of the cosine information are passedto the beam steering circuit 50 which forms the required phase tapers bygenerating for each row and column the phase difference from the zero orreference row and column in and n, respectively, referred to previously.The beam steering circuitry is comprised of positive and negative Xmultiplier circuits 51 and 52, respectively, and an X inverter 53 togenerate all the X signals by multiplying the X command by all in tegersfrom n to +12 for the total number of columns in the planar array.Likewise, the beam steering circuit 50 is comprised of a positive andnegative Y multiplier circult 54 and 55, respectively, and a Y invertercircuit 56 to multiply the Y command signals by all integers from n to+11 to provide a signal for each row of the planar array. The X and Ymultiplier circuits are preferably D.C. coupled logic circuits whichfunction as adders to form the appropriate output signals. In order toform any even numbered output (i.e., 2X, 4X, et cater-a), this may beachieved simply by shifting the bniary word 1-bit position toward theleft for multiplication by two, 12-bit position toward the left formultiplication by four, .l-bit positions to the left for multiplicationby eight, and so forth. This X multiplier circuit 52 operatessubstantially in the same manner. In order to insure that themultiplication operations have been carried out correctly, a comparatorcircuit 57 is provided for comparing +X and X outputs, 2X and +2Xoutputs, 3X and +3X outputs, et cetera. If the resultant sum of thesecomparisons is zero, operation continues in normal fashion. If thecomparison operation detects a difference signal, alarm indication isprovided at its output, which alarm indication may be employed for thepurpose of terminating operation. providing an audio-visual alarmsignal, and so forth. The +Y and Y multiplier circuits 54 and 55,respectively, also operate in a similar manner, and associated positiveand negative generated signals are likewise compared in comparatorcircuit 57 to assure generation of accurate signals.

The beam steering circuit 50 is further comprised of a spherical phasecorrection circuit 58 which is an electronic circuit for providing thenecessary phase correction for phase delays introduced due to thedifferences in distance from the antenna feed. For example, it is veryclear that electromagnetic waves will arrive at the radiating elementsat the extreme left and right-hand ends of the planar array 13, laterthan such electromagnetic waves will arrive at the radiating elementswhich like in the immediate region of the feed longitudinal axis 11'.=Output signals are thereby developed by circuit 58 for each of theradiating elements in the planar array, such that this signal. Whenadded to the phase delay correttponding to the distance of the elementto the feed, is a constant. Since these corrections are substantiallyconstant for any given antenna array the spherical correction 13 factorfor each radiating element may be pre-wired into its associated adder.

The outputs of the multiplier circuits 51, 52, 54 and 55 and thespherical phase correction circuit 58 are impressed upon the electronicmodule matrix 60 which-is a regular matrix of adder circuits such as,for example, the adder circuit 61, arranged in m columns and 21 rows,with each of these adder circuits being designed to accept theassociated X and Y input, together with the spherical phase correctioninput, to form the sum which signal is the precise phase conditionrequired by element i j in order to point the antenna in the directionsa and 5. The adder circuits such :as, for example, the adder circuit 61,may, for example, be comprised of a parallel three-binary bits outputwhich is suitably amplified and impressed upon the short-circuitingelements of the associated radiating elements to obtain the desiredphase taper.

The binary output of the scan control circuit is delivered to p bitswhen impressed upon the inputs of the X and Y multiplier circuits. Aftermultiplication of inputs by all integers corresponding to the values ofi and j, the outputs of the multiplier circuits are then quantized to rbits, where r is equal to or less than p. The outputs of the sphericalcorrection factor circuit 58 are also quantized r bits. The addercircuits such as, for example, the adder circuit 61, receives theinformation quantized to r bits and delivers the sum quantized to S bitswhere S is equal to or less than r.

Once an object has been detected during quiescent operation and it isthen desired to obtain a fix on such :an object, the electronics locksin on the desired sector. The Isophase signal is then employed at thistime to obtain very accurate data on object location.

In radar tracking operations, when more than a single pulse is returnedby a target, the several pulses are Isophase corrected during the periodof a single fix in a manner to be more fully described. Since radartargets are typically slow moving in relation to the speed ofelectromagnetic propagation and the radar pulse repetition rates beingin the order of hundreds or thousandths of pulses per second, it may beconsidered that several pulse returns from the target are being returnedfrom eifectively the same fixed position in space.

Isophase operation is obtained by employing the electronic controlcircuitry 40 in a manner such as to feed angular informationrepersenting a and 5 into the circuit S for a specific beam orientation,and Isophase signal A is then added to the terms iK cos a+jK C FH- U, 1

The magnitude of the signal A is altered prior to the generation of eachpulse to be transmitted from the antenna feed 11 so that the resultingsum l cos +i 2 cos B+ 1') 0 is a slightly different number for eachtransmitted pulse. In the circuitry of FIGURE this is obtained byproviding a constant A generating circuit 62 which is capable of eitherbeing manually or automatically controlled to develop a constant binaryoutput level. This constant binary output is fed into a summing circuit64 together with the output of a signal generator 63 so that theresulting output of summing circuit 64 is constantly changing at a ratedetermined by the signal repetition rate of the signal generator 63.Signal generator 63 may be a random signal generator, a sinusoidalsignal generator, a staircase wave signal generator, a sawtooth Wavesignal generator, or any other suitable signal generating means whichprovides a constantly changing output level with either a regular orrandom repetition rate. If desired, the constant output means 62 and sumcircuit 64 may be omitted, and the signal generator means 63 alone may14 be used to apply the Isophase signal A to each of th adder circuitsin electronic matrix 60. The output of adder circuit 64 may be convertedto binary form in any suitable manner, such as A-to-D converter 65. Ifdesired, any suitable binary output device may be employed in lieu ofthe Isophase generating circuit of FIGURE 5.

Another manner of developing the Isophase signal A is shown in FIGURES5a through 50. In the arrangement of FIGURE 5a, a clock-pulse source 66is provided for generating output pulses at a constant repetition rate.These output pulses are impressed upon the input of a first stage of amultistage binary divider or binary counter circuit 67 Where the outputsof each of its multiple stages are available at 68 for developing theIsophase signal. The output of the last stage of binary divider circuit67 is impressed upon the first stage of a second multistage binarydivider circuit 69 with the output of each of its multistages beingavailable at 70 to develop the signal K cos 0c. The binary divider, orcounter circuit 66, develops an output represented by waveform 71, shownin FIGURE 5b. For example, considering the binary divider circuit 67 asbeing comprised of four stages, the state of the output circuit forincreasing time is represented by each discrete step of the staircaseWaveform 71. As soon as the final step (i.e., the binary state 1111) isachieved, the binary divider circuit 67 automatically resets itself tobegin stepping through another complete cycle beginning at time T forexample. As soon as the binary divider circuit 67 resets itself, a pulseis provided to the input of binary divider circuit 69 at time T causingthe output to increase its count by one binary bit as represented by thestep waveform 72, shown in FIGURE 50.

The signal A is defined as the Isophase signal because it is constant invalue over the aperture of the planar array at any instant of time. Thesignal A has no effect on nominal beam angles or and 5 since it does notaffect the phase taper. If the signal A is added before finalquantization, which takes place at the aperture of the antenna and isfiner than the aperture quantization, variation in the signal in themanner taught by the circuitry of FIGURE 5a or the circuitry 62 through65 of FIG- URE 5, the variation or change in the signal A varies thedistribution of the final quantization errors.

Considering FIGURE 6 curve 73 shows the phase of the radiating elementsas a quadratic function of the radiating elements in the x direction.The curve 70 is the corrected curve which results when the sphericalcorrection factor 71 is added to the terms iK cos a. The resultinglinear phase taper is shown by (straight line) curve 75. The phase shiftwhich results from an addition of the Isophase signal A which is equalto 22.5 phase increase. The phase jumps shown by step-like curve 76occur each time a 45 phase increase occurs. For-example, the fifthradiating element to the right of the y axis is the first element tochange its phase front upon application of the Isophase signal A Byadding a constant signal A to each of the radiating elements, whichconstant signal has a value smaller than the phase differences betweenadjacent phase fronts, then there will be an insufficient amount addedto the total phase signal 15 [see Equation (1)] to cause an incrementalchange in phase between each and every adjacent radiating element.

In a system which uses Isophase to integrate out aperture quantizationerror, the beam steering computer will also accept A quantized to 1'bits, and deliver, quantized to s bits the sum of for other purposessuch as error checking, and equalization of power dissipation byswitching between states 15 which are logically identical in terms ofbeam steering, but physically different. In the above case those bits inA less significant than s are logically significant.

In a system which uses Isophase to integrate out multiplier quantizationerrors the beam steering computer will also accept A quantized to morethan r bits and add it before the multiplier quantization.

ili' cos 04+ A sl 7K COS 8+ min Wt'i'. j) p bits p bits bi? its r bits rbit-s sum quantized to .9 bits The two Isophase signals A and A need notbe identical. In each, bits less significant than p contribute tointegration of multiplier output {adder input) quantization, and,therefore, should be present in both A and A In each, bits equal to orgreater than r in significance and less than s will be transmitteddirectly to the final addition where they will integrate out aperturequantiza: tion errors. These last bits need be present in only one ofthe two Isophase signals. Those bits present in both Isophase signalsneed not vary synchronously; best integration requires them to beindependent.

In practice, the number of Isophase bits to be used will be a compromiseamong factors such as increasing cost of hardware and increasedintegration time. and asymptomatic improvements as the number of bitsused is increased. For integration of either aperture or adderquantization errors, the most significant bit or" those logicallysignificant will have the greatest smoothing effeet, and this smoothingeifect will decrease with decreasing significance.

Isophase conceivably can be used in another manner. It is evident thatfor any pair of input signals K. a and K2 cos 5 there will be certainIsophase signals which will produce minimum error, and that theseoptimum Isophase signals will vary with K cos a and 1K? cos a. It may bepossible by the use of a computer to determine a relationship betweenthe input signals and the optimum Isophase signals. If the relationshipis simple, a simple computational device will be able to generate andapply the optimum lsophase signals from the input signals. if therelationship is more involved, a precompute-d tabulation with look-upmay be practical.

The Isophase signal may be employed in substantially the same manner ashas been described above to provide other novel functions. For example,in the case of antenna systems installed in moving objects such as. torexample, marine craft, the pitch, yaw, and roll of the ship contributeto unwanted movement of the antenna array. The Isophase output of FIGURE5 may then be combined with or substituted by the outputs of suitableattitude control synchro generators 80, 81, 32 for generating signalsrepresentative of instantaneous changes in pitch, yaw and roll detectedby circuits 3335, respectively, generating signals of equal magnitudeand opposite polarity to compensate for changes in pitch. yaw and rollso as to develop a resulting signal to efiectively electronicallyoperate the antenna array to simulate a stationary mounted antennasystem. Any other changes in attitude of other craft such as aircrat'tsmay also be emloyed for the correction of change in attitude of theantenna assembly so that its operation simulates a stationary mountedsystem.

It can be seen from the foregoing that the instant invention provides anovel electronic control means which employs a time-changing lsophasesignal which is constant over the antenna array at any given instant soas not to substantially alter the phase taper of the electromagneticwave front, but which shifts the location or changes in phase along theaperture and which averages a plurality of returning pulses to therebyproduce a resultant averaged signal which greatly diminishes beampointing error and unwanted sidelobe effects.

The addition of several Isophase signals to the o: and 5 data and thespherical correction factor data at one beam pointing position causesthe beam to deviate slightly about a nominal beam pointing position. Thereturning signals from the target are then integrated by use of aplan-position indicator scope having long persistent characteristics andtogether with the observers eye provides the desired integration of theslight variation in returning signals. A variety of Isophase valuesprovided both positive and negative movement about the nominal beamdirection causing smoothing of unwanted sidelobes and improvement inbeam pointing.

The Isophase signals also have the advantageous side eifects orequalizing power dissipation over the antenna aperture and averaging outthe elfects of mutual coupling between tthe radiating elements surfacereflections and element random phase errors.

Whereas the description given herein relates to an active antenna systemwhich transmits electromagnetic radiation for tracking objects, itshould be understood that the antenna array may be operated in a passivemanner by controlling the phase of the radiating elements to preciselytrack objects such as active satellites which transmit their ownsignals.

Although this invention has been described with respect to its preferredembodiments, it should be understood that many variations andmodifications will now be obvious to those skil ed in the art, and it ispreferred, therefore, that the scope of the invention be limited not bythe specific disclosure herein, but only by the appended claims.

What is claimed is:

ii. In an antenna system comprising a stationary array of radiatingelements, a feed means for directing elect-romagnetic waves generated ata predetermined repetition rate toward said array to produce a beam;phase control means selectively coupled to said radiating elements forcontrolling the phase delay of the radiating elements in the array tocause the beam to scan a region in space, the improvement comprisingfirst means for producing a signal which is simultaneously coupled toall of said radiating elements for altering the phase delay imposed uponthe electromagnetic waves by said phase control means; said first meansincluding second means for altering the magnitude of said signal at arate at least as rapid as the repetition rate of said feed means.

2. The system of claim 1 wherein said first means includes means forgenerating at least two successive signals of differing magnitude.

.3. The system of claim 1 wherein said output of said first means is inparallel binary bit form comprised of at least two binary bits.

4. The system of claim 3 wherein said first means is comprised of a highfrequency oscillator means; said second means being comprised of amultistage binary divider for generating a parallel a bit output where aequals the number of stages of said binary divider.

5. The system of claim 1 wherein said radiating elements are comprisedof third means for reflecting said electromagnetic Waves after a firstpredetermined phase delay; and fourth means under control of said firstmeans for selectively altering the first phase delay.

o. The system of claim 5 wherein said first means is comprised of fifthmeans for generating binary signal groups for each of said radiatingelements to control the pointing of said beams through alteration of thephase delay by each of said radiating elements.

7. The system of claim 1 further comprising means coupled to each ofsaid radiating elements for generating spherical correction factorsignals to correct for differing phase delays introduced by saidradiating elements due to their diflering distances from the feed means.

h. The system of claim 6 further comprising sixth means coupled to eachof said radiating elements for generating spherical correction factorsignals to correct for 17 differing phase delays introduced by saidradiating elements due to their difiering distances from the feed means.

9. The system of claim 6 wherein said fourth means is comprised of meansfor summing the outputs of said phase control means and said first meansto generate an output signal; said fourth means including a plurality ofshort-circuiting means selectively controlled by said output signal toalter said first phase delay.

10. The system of claim 8 wherein said fourth means is comprised ofmeans for summing the outputs of said phase control means, said sixthmeans and said first means to generate an output signal; said fourthmeans including a plurality of short-circuiting means selectivelycontrolled by said output signal to alter said first phase delay.

11. The system of claim 1 wherein said first means is further comprisedof sensing means for sensing the attitude of said system when mountedupon a movable surface; means coupled between said attitude sensingmeans and said radiating elements for generating compensating outputsignals when a change in attitude is detected, controlling saidradiating elements to cause said planar array to operate as though nochange in attitude has occurred.

12. An antenna system comprising a stationary array of receivingelements;

feed means for receiving electromagnetic Waves refiected from said arraytoward said feed means to provide a receiver beam;

means for controlling the phase delay of the elements to cause the beamto scan a region in space, each of the elements having input means forreceiving the signals controlling the scan in space;

the improvement comprising first means to simultaneously deliver thesame signal to the input means of each element to alter the phase delayimparted to the electromagnetic waves by said phase delay control meansand second means to cause said signal delivered to the input means tovary in either a controlled or random manner.

13. An antenna system comprising a stationary array of radiatingelements;

feed means for directing electromagnetic Waves toward said array toproduce a transmitted beam, means for selectively controlling the phasedelay of the radiating elements to cause the beam to scan a region inspace;

each of the elements having input means for receiving the signalscontrolling the scan in space from said scan controlling means;-

the improvement comprising first means for simultaneously delivering thesame signal to the input means of each element to alter the phase delayimparted to the electromagnetic waves by said phase delay control meansand second means to cause the signal delivered to the input means tovary in either a controlled or random manner.

References Cited UNITED STATES PATENTS 3/1966 Vogt 343-100 8/1966Brightrnan et a1. 343-l00 11/1966 Howard 34310O 2/ 1967 Miccioli et a1.343-100

